The invention relates to new and useful improvements in data transmission. More particularly, the invention relates to a method for the clocked serial data transmission of data blocks of identical block length.
A data transmission system ought to enable data to be transmitted as fast as possible and as free from errors as possible. The data are usually transmitted with a predetermined transmission speed, the xe2x80x9cbaud ratexe2x80x9d, at which data blocks of identical block length are transmitted bit by bit and serially from a sending device to a receiving device.
In the context of digital data transmission, in particular, a data block usually has bit sequences for a header, as well as useful data and a conclusion criterion. The header usually contains details concerning the block length, while the conclusion criterion has a bit sequence which is defined in a transmission protocol. Since the data block has a defined length, control criteria are accommodated in particular in the bit sequence which is reserved for the useful data of a data block. The control criteria are used in the receiving device in particular to check correct transmission. These criteria include, by way of example, a check bit, a so-called xe2x80x9cparity bitxe2x80x9d. If the length of the bit sequence reserved for the useful data of a data block is e.g. eight bits, thus forming a byte, then specific bit combinations are reserved for special declarations and are not available for the actual transmission of the useful data. Consequently, the entire range of bit combinations from 0 to 255, or from 00 to FF, cannot be transmitted in a data block.
Therefore, efforts are generally made to transmit data with long data blocks. The purpose is to attain a faster transmission speed than with data transmission using short data blocks.
One disadvantage is that long data blocks have a correspondingly higher probability of experiencing interference during transmission and of being transmitted with errors. The entire data block must then be resent. Furthermore, particularly when there is periodic interference on the transmission link between the sending and receiving devices, error-free transmission may prove to be impossible if the clock frequency of interference pulses is above the clock frequency for the transmission of a data block. A transmission link subjected to such interference must then be provided with interference suppression by means of electromagnetic shielding measures.
U.S. Pat. No. 5,142,538 discloses a transmission method in which a data block is transmitted by a sender to a receiver and returned by the receiver to the sender. The data block sent originally and the data block received again are compared in the sender, to check that the data have been transmitted correctly. If the received data block does not correspond to the sent data block, then the data block is retransmitted. The transmission method is based on monodirectional data transmission with a so-called SIMPLEX-like mode in which the data are transmitted either from the sender to the receiver or from the receiver to the sender.
Publication WO 91/16697 discloses a transmission protocol for a data transmission device between a sender and a receiver. In this case, each data bit transmitted by the sender to the receiver is transmitted back from the receiver to the sender. If the data bits transmitted back do not correspond to the data bits sent originally, a control character is communicated to the receiver. This alerts the receiver to the fact that the faulty data will be retransmitted.
It is therefore an object of the invention to provide a method for data transmission which is faster and less sensitive to interference than conventional methods.
This and other objects are achieved by a method for clocked serial data transmission of data blocks of identical block length between a first and a second transmission device. According to one formulation of the invention, the method includes:
a) sending a data block as a sent data block in a first block cycle from the first to the second transmission device,
b) receiving the data block as a received data block at the second transmission device, and returning the received data block as a returned data block to the first transmission device,
c) receiving the returned data block at the first transmission device, comparing the returned data block with the sent data block, and generating a comparison result during a second clock cycle,
d) in a third clock cycle,
d1) in case of a comparison result signaling correspondence, continuing the data transmission from the first to the second transmission device by sending a further data block, or
d2) in case of a comparison result signaling non-correspondence, suspending the data transmission from the first to the second transmission device for the third clock cycle, and
e) in the second transmission device,
e1) in case of a detection of a single clock cycle with suspended data transmission, overwriting the received data block received in the first clock cycle with a next subsequent received data block following the suspended data transmission, or
e2) in case of a detection of two successive clock cycles with suspended data transmission, overwriting the received data block and a data block received immediately following the received data block with the next subsequent received data block following the suspended data transmission and another data block received immediately following the next subsequent received data block, respectively.
An advantage of the method of the invention is that fast and virtually error-free data transmission can take place even when there is interference on the transmission link. This is advantageous particularly in the case of transmission links which cannot be shielded against interfering influences or can be shielded only to a limited extent by means of EMC measures. Examples of such poorly shieldable transmission links are infrared transmission links or copper transmission links that cannot be shielded. In optical transmissions, the interference may occur, by way of example, due to a fluorescent lamp being switched on and/or flickering. In the context of shipbuilding, by way of example, power current-carrying lines are frequently laid, unavoidably, in the vicinity of signal or control lines. The high currents in the power current lines may then interfere with the data transmission on the signal or control lines.
A further advantage of the method of the invention is that the useful data contained in data blocks need no longer have bit combinations with special declarations for transmission error detection. This free configuration of the content of all the useful data bits contained in data blocks is advantageously possible because specific control information items which report or interrupt or stop a data flow subjected to interference need not be transmitted.
A further advantage of the method of the invention is that intermission times are reduced to a minimum between two successively transmitted data blocks. A data block received with errors can be corrected immediately.
The data transmission for the method according to the invention can take place in a mode similar to the so-called DUPLEX mode. Sending and receiving operations between a first and a second transmission device can take place simultaneously in both transmission directions. As a result, in the method of the invention, the return reception of data blocks for checking purposes is possible at the same time as the sending of data blocks. The preferably relatively short data blocks enable each individual data block to have an advantageously short transmission duration. The transmission can thus take place with a high clock frequency. If a data block is subjected to interference during transmission, then only this short data block need be transmitted again. Particularly fast correction can thus be effected. Consequently, the method according to the invention enables data transmission even when there is periodic interference on the transmission link between the sending and receiving devices.
A further advantage is that electronic components necessary for sequence control for implementing the method of the invention can be realized in particular with an integrated circuit, for example an ASIC.